Variable brightness light generators

Abstract

There is disclosed a variable brightness light generator embodied in apparatus for exposing photographic film for test purposes. The generator includes a spherical mirror, a lamp at the center of the spherical form of the mirror and a modulator located between the lamp and the mirror for modulating the brightness of the image of the lamp created on the lamp by the mirror. The intensity of the light issuing from the lamp is sensed by a spectroradiometer which produces signals used in controlling the modulator whereby the intensity may be kept constant. The color temperature of the lamp is controlled under the influence of signals from the spectroradiometer. The exposing apparatus also includes a plurality of filters selectively insertable in the light path for modifying the intensity and color of the light incident on the film.

What is claimed is: 
     
       1. A variable brightness light generator, including: a spherical mirror;   a lamp located at the center of the spherical form of said mirror; and   a modulator located between the lamp and the mirror for modulating the brightness of the image of the bulb on the bulb.   
     
     
       2. A variable brightness light generator as claimed in claim 1, wherein: said modulator is of the variable aperture type. 
     
     
       3. A variable brightness light generator as claimed in claim 3, wherein the variable aperture modulator includes two shutters movable towards and away from one another. 
     
     
       4. A variable brightness light generator as claimed in claim 3, wherein: said two shutters are formed of the same material as the reflective surface of the mirror whereby light whether reflected by the mirror or the shutters has the same spectral composition. 
     
     
       5. A variable brightness light generator as claimed in claim 4, wherein: the material of the shutters and of the reflective surface of the mirror is aluminum and the surfaces of the shutters are diffusely reflective. 
     
     
       6. A variable brightness light generator as claimed in claim 3, wherein: said modulator further includes a stepping motor for moving one blade in its plane, and a lever acting between the two blades to transmit motion from said one blade to the other blade but with the motion of said other blade being opposite in direction to that of said one blade. 
     
     
       7. A variable brightness light generator as claimed in any one of claims 1 to 6, wherein: said light bulb is of of the low voltage tungsten halogen type, whereby the filament may be small.